Analog and digital audio signals are transmitted over balanced and shielded twisted pair cables. These cables include a pair of insulated conductors, either stranded or solid wire, which are surrounded by a metal foil shield. The shield serves to reduce the impact of external electromagnetic inference on the signal being transmitted over the cable and also to reduce the electromagnetic field generated by the signals being transmitted over the cable.
In a professional audio and video industry application, a large number of such cables will be in use to carry signals from sources to processing devices such as mixers or equalizers and further to amplifiers or other downstream devices. The environment in which these signals are generated is quite dynamic and requires the ability to quickly and easily shift connections between sources, and and downstream devices. A jack field provides this sort of connection flexibility. A jack field allows incoming signals to be patched into circuits connected to devices and signals returning from devices to be patched into circuits connected to downstream devices. Each jack in this jack field requires three conducting paths, two for the balanced audio signal and one for the shield to serve as a grounding path. There are three principal ways to connect these jacks to one another, depending on the needs of the particular situation.
First, a jack field may be set up for non-normal connections, meaning that each jack is connected directly to another jack. When a connection between devices is needed, a patch cord must be used. For example, a source is connected to J1 and J1 is electronically linked to jack 1. A device is connected to J1 and J2 is electronically linked to jack 2. To link the source to the device, a patch cord would be used to electronically link jack 1 to jack 2, as shown in FIG. 28b. Without a patch cord in place in jack 1 or jack 2, no connection will exist for either the source or the device, as shown in FIG. 28a. 
A second method of connecting jacks is referred to as normal. As an example, a source and an device are designated to be linked together electronically as a default or normal condition, but it is still necessary to be able to switch the source to another device, or connect another source to the device, on occasion. To accomplish this, a source is connected to J1 and an device is connected to J2. J1 is also electronically connected to J2. Jacks 1 and 2 are placed in the circuit connecting J1 and J2, as shown in FIG. 29a, and are configured such that, if a patch cord is inserted into jack 1 or jack 2, the connection between J1 and J2 is broken, as shown in FIG. 29b. If a patch cord is inserted into jack 1, it will not only break the J1–J2 connection, but the patch cord will be electronically linked to the source connected to J1. Similarly, a patch cord inserted into jack 2 will break the J1–J2 connection and be electronically linked with the device connected to J2. So, in a normal configured jack field, two elements can be configured to be normally electronically connected to one another but that normal connection can be broken and the connections redirected as necessary.
A third method of connecting jacks is referred to as half-normal. In the default state, a source connected to J1 and an device connected to J2 are connected together through jack 1 and jack 2, as shown in FIG. 30a. This arrangement allows, for example, the feed coming from a source to J1 to be monitored by a device connected into the normal circuit by a patch cord inserted into jack 1 without the insertion of the patch cord into jack 2 causing the connection between the source and the device connected to J2 to be broken, as shown in FIG. 30b. In addition, the connection between the source and the device can be broken by the insertion of a patch cord in jack 2. When a patch cord is inserted into jack 2, the patch cord in jack 1 can then be used to patch the source to another device and patch cord in jack 2 can be used to patch another source to the device, as shown in FIG. 30c. 
Another aspect of the connection between jacks and devices connected to the jacks is the treatment of the shield. Typically, the shield of the cable connected to the first jack is electronically linked to the shield of the cable connected to the second jack when the first jack and the second jack are electronically linked. It is desirable to have the ability to link the shields either individually or jointly to a common ground. This allows maximum flexibility in the configuration in the electronic linkages between the jacks, depending on the devices connected to the jacks.
While these connection schemes within a jack field are known, the ability of users to reconfigure a jack field or a jack pair within a jack field from one to another of the three arrangements could be improved. A variety of approaches have been used in the past, including wire wrapping leads together between the jacks, soldering the leads together between the jacks, using straps or jumpers to reconfigure connections between jacks, or using small metal plates of different sizes and shapes to reconfigure the connection between jacks. In some designs, the entire jack field would need to be exchanged to reconfigure the arrangement. This type of design does not allow the users to configure the circuits connected to individual devices and required all devices connected to a particular jack field to be configured identically. Improvement to the ability to create and modify the state of the connection between jacks and individual devices in the jack fields is desirable.
In addition, users of these types of devices and jack fields have very complex and dense wiring environments within their physical plants. Improvement to the density of connections possible in the limited space available within their physical plant without a loss of flexibility of configuration is desirable.